The present invention relates to a laminated piezoelectric transformers for use in cold-cathode-tube inverter circuits, which are used in electronic apparatuses having a liquid crystal screen such as personal computers, portable information terminals and video movies, for stepping up voltages and lighting/dimming the cold cathode tube or for use in other voltage stepping up circuits.
A method of fabricating a conventional laminated piezoelectric transformer will be described below. FIG. 18 is a perspective view of a conventional laminated piezoelectric transformer.
First, ceramic layers 111 and input side internal electrodes are alternately laminated to form a laminated body in a rectangular parallelepiped shape. At this time, the internal electrodes on the input side (primary) are arranged to be alternately exposed on the opposite side faces of the laminated body at the middle portion along the longitudinal direction of the laminated body.
Then, primary external electrodes 112 are formed on both the side faces where the primary internal electrodes are exposed and, meanwhile, external electrodes 113 on the output side are formed on both end faces of the laminated body and, thus, a laminated piezoelectric transformer is produced. According to this structure, since external electrodes 113 on the output side (secondary) are provided perpendicularly to the direction of oscillation of the laminated piezoelectric transformer, there has been such a problem that the oscillations are attenuated and hence the energy conversion efficiency is deteriorated.
It is an object of the present invention to provide a piezoelectric transformer capable of stepping up voltages at high energy conversion efficiency.
A laminated piezoelectric transformer according to the present invention comprises:
a laminated body formed by laminating a plurality of ceramic layers and a plurality of internal electrodes; and
a plurality of external electrodes electrically connected to the internal electrodes and disposed on the surface of the laminated body.
Further, the internal electrodes of the laminated piezoelectric transformer of the invention are characterized by having a plurality of primary internal electrodes disposed at the middle portion along the longitudinal direction of the laminated body and a plurality of secondary internal electrodes disposed at opposite end portions of the laminated body with respect to the longitudinal direction. By virtue of this configuration of the invention, the polarization volume on the output side can be enlarged and, therefore, the laminated piezoelectric transformer of the invention can step up voltages at high energy conversion efficiency.